The present invention generally relates to power boosters for brake systems, such as those used in automobiles, for intensifying the input force between a brake pedal and a master cylinder.
Brake power boosters generally utilize fluid pressure, or differentials thereof, to provide a power assist in applying force to the master cylinder of the brake system. Upon application of an input force on the brake pedal, an input member such as a pushrod activates the power booster. The power booster intensifies the force by a calibrated amount and transfers the force to a power piston which then moves the master cylinder to apply the brakes at each wheel.
In conventional power boosters, an air valve assembly is opened upon depression of the brake pedal by the operator to admit atmospheric air to at least a first chamber of the power booster housing. This creates a pressure differential across a diaphragm separating the first chamber from a second chamber of the housing. The diaphragm is coupled to the power piston and transmits a force resulting from the pressure differential to the power piston and, ultimately, to the master cylinder.
The force generated by the power booster is a function in large part to the volume of the working chambers of the power booster housing. As a result, the use of vacuum boosters of this type have been limited by physical space constraints, particularly with respect to the booster diameter. Larger and/or heavier vehicles such as trucks and the like require substantially more output force to adequately stop the vehicle. Known vacuum boosters have not been able to deliver the required output force within the available physical size constraints. Therefore, typically a hydraulic booster is employed in larger and/or heavier vehicles to produce sufficient output force to adequately stop such vehicles.
For these general reasons, it would be desirable to provide a vacuum power booster that delivers a high output force to the master cylinder for larger and/or heavier vehicles such as trucks and the like without exceeding the physical space constraints that are available, particularly with respect to booster diameter. Moreover, due to the relatively large number of parts required for a typical power booster and the wide range and styles of automobiles utilizing such systems, the inventory, assembly, repair and related requirements place significant demands on the brake system manufacturer and repair technician. Therefore, it would be highly desirable to provide such a power booster without significantly adding to the inventory, assembly and service demands of such a system.
The present invention generally provides a vacuum power booster for a brake system with an air valve assembly having the ability to deliver a high output force within limited available space. The present invention could be used for vehicles where a larger vacuum booster is needed, but there is a constraint on booster diameter. Furthermore, the invention offers these advantages while minimizing the number of unique parts and assembly or service demands.
In one embodiment, this invention is a triple vacuum booster in which an additional working chamber is added to known dual chamber vacuum booster. The invention increases output force by approximately 45% over known vacuum boosters having a comparable booster diameter. The present invention utilizes many of the same components of known tandem boosters and as such provides a very economical solution to increase booster output without adding significantly to production costs, inventories and support requirements.
Generally, the power booster of this invention includes a housing having an interior and a number of diaphragms and associated plates separating the interior of the housing into at least three chambers. A two-piece power piston is coupled for movement with the diaphragms and includes an output rod. An input member is adapted to be coupled to a movable brake pedal and is coupled to an air valve assembly. The input member moves the air valve assembly between open and closed positions to selectively admit atmospheric air into at least one of the chambers to induce an output force on the diaphragms which is transferred to the output rod of the power piston.
In accordance with the invention, the vacuum booster includes first, second and third chambers in which the first and second chambers are of comparable size and design with respect to known tandem boosters. The third chamber similarly sized with respect to the first and second chambers or may have a reduced size booster for applications where additional boost is required over a comparable tandem booster, but packaging limitations dictate a reduced size third chamber. Advantageously, the assembly of the triple booster utilizes a number of identical components for the multiple chambers thereby minimizing inventory complexities. Moreover, the installation of the diaphragms entails a retaining ring or similar member to both seal the diaphragm to the power piston and secure the multi-component power piston assembly together.
Testing of the triple booster according to this invention has shown that input/output force plots are substantially identical with respect to tandem booster designs with the exception of an increase in overall output force on the order of about 45%. This offers a significant benefit in braking force without the need for new calibration and tuning procedures typically required for new booster designs.